Effect of Interocular Contrast Difference on Stereopsis in Observers With Sensory Eye Dominance

Integration and suppression interact in binocular vision

Contingent on stereo compatibility, two images presented dichoptically can lead to either binocular integration, thus generating stable stereopsis, or interocular suppression that induces binocular rivalry with bistable perception that alternates between the two images. The relationship between binocular integration and interocular suppression concerns how our brain processes binocular inputs to form unified visual awareness but remains unclear. Here, a series of psychophysical experiments were conducted to address this question, revealing that these collaborative and competitive binocular interactions are interconnected and would mediate one another according to their strength. Specifically, Experiments 1a and 1b showed that the presence of binocular rivalry inhibited peripheral stereopsis, significantly elevating the stereo threshold, with higher elevation resulting from increasing rivalry contrast. Experiments 2a and 2b showed that existing stereopsis with increasing binocular disparity balanced the dynamics of peripheral binocular rivalry, rendering more equivalent eye dominance. Based on these interactions, we suggest that binocular integration and interocular suppression may mediate one another through an overlapping mechanism for regulating eye dominance, with strong stereo percepts tending to reduce eye dominance and strong rivalry tending to increase eye dominance.

Influence of Interocular Differences and Alcohol Consumption on Binocular Visual Performance

The purpose of this study was to assess the influence of a moderate breath-alcohol content (BrAC of 0.40 mg/L) on binocular visual performance for different visual functions after inducing different levels of interocular differences with the use of filters. A total of 26 healthy young subjects were enrolled. The participants participated in two sessions: one without alcohol consumption and another after alcohol consumption. In each session and for the different filter conditions (subjects were wearing Bangerter foil of 0.8 and BPM2 fog filter on the dominant eye), monocular and binocular visual function was evaluated by measuring visual acuity, contrast sensitivity, visual discrimination capacity (and successively by calculating their corresponding binocular summations) and stereopsis (near and distance stereoacuity). In addition, interocular differences were calculated for different retinal-image quality and straylight parameters. All monocular and binocular visual functions were analyzed and stereopsis was significantly impaired by alcohol and filters (p < 0.05). Interocular differences for different ocular parameters and binocular summations for visual parameters were negatively affected by filters but not alcohol. Significant correlations (averaging all the experimental conditions analyzed) were found, highlighting: the higher the interocular differences, the lower the binocular summation and the poorer the stereopsis and, therefore, the worse the binocular visual performance.

Recent understanding of binocular vision in the natural environment with clinical implications

Technological advances in recent decades have allowed us to measure both the information available to the visual system in the natural environment and the rich array of behaviors that the visual system supports. This review highlights the tasks undertaken by the binocular visual system in particular and how, for much of human activity, these tasks differ from those considered when an observer fixates a static target on the midline. The everyday motor and perceptual challenges involved in generating a stable, useful binocular percept of the environment are discussed, together with how these challenges are but minimally addressed by much of current clinical interpretation of binocular function. The implications for new technology, such as virtual reality, are also highlighted in terms of clinical and basic research application.

Sensory Eye Dominance: Relationship Between Eye and Brain

Eye dominance refers to the preference to use one eye more than the fellow eye to accomplish a task. However, the dominant eye revealed can be task dependent especially when the tasks are as diverse as instructing the observer to sight a target through a ring, or to report which half-image is perceived more of during binocular rivalry stimulation. Conventionally, the former task is said to reveal motor eye dominance while the latter task reveals sensory eye dominance. While the consensus is that the motor and sensory-dominant eye could be different in some observers, the reason for it is still unclear and has not been much researched. This review mainly focuses on advances made in recent studies of sensory eye dominance. It reviews studies conducted to quantify and relate sensory eye dominance to other visual functions, in particular to stereopsis, as well as studies conducted to explore its plasticity. It is recognized that sensory eye dominance in observers with clinically normal vision shares some similarity with amblyopia at least at the behavioral level, in that both exhibit an imbalance of interocular inhibition. Furthermore, sensory eye dominance is probably manifested at multiple sites along the visual pathway, perhaps including the level of ocular dominance columns. But future studies with high-resolution brain imaging approaches are required to confirm this speculation in the human visual system.